Added Nearley-to-lark converter

lark/common.py

@@ -13,10 +13,13 @@ class UnexpectedToken(ParseError):
         self.line = getattr(token, 'line', '?')
         self.column = getattr(token, 'column', '?')
 
-        context = ' '.join(['%r(%s)' % (t.value, t.type) for t in seq[index:index+5]])
+        try:
+            context = ' '.join(['%r(%s)' % (t.value, t.type) for t in seq[index:index+5]])
+        except AttributeError:
+            context = seq[index:index+5]
         message = ("Unexpected token %r at line %s, column %s.\n"
                    "Expected: %s\n"
-                   "Context: %s" % (token.value, self.line, self.column, expected, context))
+                   "Context: %s" % (token, self.line, self.column, expected, context))
 
         super(ParseError, self).__init__(message)
 

tools/nearley.py

@@ -0,0 +1,124 @@
+"Converts between Lark and Nearley grammars. Work in progress!"
+
+from lark import Lark, InlineTransformer
+
+nearley_grammar = r"""
+    start: (ruledef|directive)+
+
+    directive: "@" NAME STRING
+    ruledef: NAME "->" expansions
+    expansions: expansion ("|" expansion)*
+
+    expansion: (rule|string|regexp)+ _JS?
+
+    rule: NAME
+    string: STRING
+    regexp: REGEXP
+    _JS: /(?s){%.*?%}/
+
+    NAME: /[a-zA-Z_]\w*/
+    WS.ignore: /[\t \f\n]+/
+    COMMENT.ignore: /\#[^\n]*/
+    REGEXP: /\[.*?\]/
+    STRING: /".*?"/
+
+    """
+
+
+
+class NearleyToLark(InlineTransformer):
+
+    def rule(self, name):
+        return {'_': '_WS?', '__':'_WS'}.get(name, name)
+
+    def ruledef(self, name, exps):
+        return '%s: %s' % (name, exps)
+
+    def regexp(self, r):
+        return '/%s/' % r
+
+    def string(self, s):
+        # TODO allow regular strings, and split them in the parser frontend
+        return ' '.join('"%s"'%ch for ch in s[1:-1])
+
+    def expansion(self, *x):
+        return ' '.join(x)
+
+    def expansions(self, *x):
+        return '\n    |'.join(x)
+
+    def directive(self, name, *args):
+        if name == 'builtin':
+            arg = args[0][1:-1]
+            if arg == 'whitespace.ne':
+                return r'_WS: /[ \t\n\v\f]/'
+            elif arg == 'number.ne':
+                return ('unsigned_int: DIGIT+\n'
+                        'DIGIT: /\d/\n'
+                        'decimal: "-"? DIGIT+ [/\./ DIGIT+] \n'
+                        'percentage: decimal "%"\n'
+                        )
+                # TODO
+            elif arg == 'postprocessors.ne':
+                pass
+            else:
+                assert False, arg
+        else:
+            assert False
+        pass
+
+    def start(self, *rules):
+        return '\n'.join(filter(None, rules))
+
+def nearley_to_lark(g):
+    parser = Lark(nearley_grammar)
+    tree = parser.parse(g)
+    return NearleyToLark().transform(tree)
+
+
+def test():
+    css_example_grammar = """
+# http://www.w3.org/TR/css3-color/#colorunits
+
+    @builtin "whitespace.ne"
+    @builtin "number.ne"
+    @builtin "postprocessors.ne"
+
+    csscolor -> "#" hexdigit hexdigit hexdigit hexdigit hexdigit hexdigit {%
+        function(d) {
+            return {
+                "r": parseInt(d[1]+d[2], 16),
+                "g": parseInt(d[3]+d[4], 16),
+                "b": parseInt(d[5]+d[6], 16),
+            }
+        }
+    %}
+              | "#" hexdigit hexdigit hexdigit {%
+        function(d) {
+            return {
+                "r": parseInt(d[1]+d[1], 16),
+                "g": parseInt(d[2]+d[2], 16),
+                "b": parseInt(d[3]+d[3], 16),
+            }
+        }
+    %}
+              | "rgb"  _ "(" _ colnum _ "," _ colnum _ "," _ colnum _ ")" {% $({"r": 4, "g": 8, "b": 12}) %}
+              | "hsl"  _ "(" _ colnum _ "," _ colnum _ "," _ colnum _ ")" {% $({"h": 4, "s": 8, "l": 12}) %}
+              | "rgba" _ "(" _ colnum _ "," _ colnum _ "," _ colnum _ "," _ decimal _ ")" {% $({"r": 4, "g": 8, "b": 12, "a": 16}) %}
+              | "hsla" _ "(" _ colnum _ "," _ colnum _ "," _ colnum _ "," _ decimal _ ")" {% $({"h": 4, "s": 8, "l": 12, "a": 16}) %}
+
+    hexdigit -> [a-fA-F0-9]
+    colnum -> unsigned_int {% id %} | percentage {%
+        function(d) {return Math.floor(d[0]*255); }
+    %}
+    """
+    converted_grammar = nearley_to_lark(css_example_grammar)
+    print converted_grammar
+
+    l = Lark(converted_grammar, start='csscolor', parser='earley_nolex')
+    print l.parse('#a199ff').pretty()
+    print l.parse('rgb(255, 70%, 3)').pretty()
+
+
+if __name__ == '__main__':
+    test()